This invention relates to the beneficiation of lignite. In one of its aspects it relates to the recovery of lignite having a substantially reduced mineral matter or ash content. In another of its aspects the invention relates to a specially designed apparatus for beneficiating lignite.
In one of its concepts the invention provides a method for beneficiating lignite by removing therefrom clay or other mineral matter which comprises crushing a lignite, introducing the crushed lignite into an upwardly inclined conveyor-agitator-washing zone, conveying it upwardly through the zone while agitating, and bringing the lignite into intimate contact with a washing or cleaning medium e.g., water, under agitating conditions sufficient to fracture the lignite; allowing cleaning medium to move downwardly through said zone, maintaining a relatively quiescent section at the lower end portion of the zone, allowing lignite to settle to the bottom of the quiescent section, removing lignite from the bottom of the quiescent section without disturbing unduly its quiescent state, conveying the removed lignite upwardly through the zone and removing supernatant washing medium containing undesired impurities suspended therein from the bottom portion of the zone while removing cleaned lignite from the upper end of the zone. In a more specific concept of the invention it provides a smooth flight or blade equipped screw portion extending through the quiescent zone and a notched or otherwise structured agitator-conveyor portion on the remainder of the screw, as further described below.
The art of conveyors, washers and apparatus for removing water from ores and for removing shale and coal from gravel is replete with a great many different and many similar disclosures of methods and apparatus. U.S. Pat. No. 992,629 issued May 16, 1911, shows an apparatus for dewatering and classifying ores in which rotation of a continuous spiral agitates a pulp and causes lighter particles of ore or slimes to be retained in suspension with the coarser particles settling through the liquid. Interrupted spiral flights or rabbles cause the heavier particles of ore which have settled to the bottom of a tank and which have been conveyed to the end of the continuous spiral, to be carried to a sand-delivery end with water and lighter particles draining back through the interrupted spirals.
U.S. Pat. No. 2,216,371 issued Oct. 1, 1940, for apparatus for removing shale, coal, and the like from gravel discloses an apparatus wherein at a lower end thereof water is passed upwardly into an agitating section and out the top of this section from which the introduced material is upwardly conveyed by a continuous flight. U.S. Pat. No. 3,739,911, issued June 19, 1973, discloses a pool-less auger-separator for material of differing specific gravities. The patent shows the moving of heavier substances upwardly with an auger in a trough while pieces of lighter substance which can be as large as lump coal are pushed by the force of turbulent, pool-less, free-flowing water out of an open lower end of the trough. U.S. Pat. No. 1,412,010, issued Apr. 4, 1922, for an ore classifier, shows on the same shaft a continuous spiral and spiral flights having rabbles or blades which serve to convey material toward a more elevated portion of the apparatus, agitating as each succeeding blade tends to have a plying effect upon the material left by the preceding blade while the liquid in the apparatus can drain freely back through and between the rabbles or interruped spirals. An overflow weir over which slime and lighter particles overflow is shown at the lower end.
In Ser. No. 364,586 filed of the same date herewith by Cecil C. Gentry and Henry E. Alquist and commonly assigned herewith there is disclosed and claimed a method for removing from lignite a substantial portion of mineral matter or ash content originally associated therewith which comprises feeding crushed lignite into a lower-end portion of an upwardly inclined conveyor treating zone, in this zone subjecting the lignite to agitation and consequent fracturing while simultaneously subjecting the lignite to the action of a cleaning or washing medium, removing treated lignite from an upper-end portion of the zone; permitting settling of lignite from the medium now containing ash-producing particles suspended therein, at the lower-end portion of the zone below the locus of introduction of the crushed lignite; conveying the lignite upwardly through the zone; and removing cleaning medium, now supernatant the lignite, from the lower-end portion of the zone.
Also disclosed and claimed in the copending application is an apparatus comprising in combination a conveyor section, a conveyor screw within this section, means for introducing into a lower-end portion of the apparatus a crushed material to be cleaned therein, means for causing the conveyor screw to convey crushed material upwardly through the apparatus, means at the upper-end of the apparatus for removing cleaned material herefrom, means associated with the apparatus for supplying a cleaning medium to the crushed material therein while it is being upwardly conveyed by the conveyor screw and agitated thereby, a quiescent section at a lower-end portion of the apparatus below the point of introduction of the material to be cleaned to permit settling of the cleaned material to provide a supernatant phase of cleaning medium and means for removing the supernatant phase from the apparatus.
I have now conceived that the separation in the quiescent section can be effectively accomplished while simultaneously providing considerably increased flexibility of operation in the fracturing and washing of the crushed lignite in the fracturing and washing section of the overall zone e.g., wider rotational speed limits, by providing means or operating methods for removing the settled lignite from the quiescent section by employing a screw conveyor sectioned as herein described.
An object of this invention is to beneficiate lignite. Another object of this invention is to provide a method for removing mineral matter or ash content from lignite. A further object of the invention is to provide a method for removing mineral matter from a lignite into a washing medium and recovering said washing medium from lignite without loss of the lignite into the washing medium while at the same time producing a lignite of substantially reduced mineral matter content.
Other aspects, concepts, objects, and the several advantages of this invention are apparent from a study of this disclosure, the drawings and the appended claims.